The present invention relates to a travelling wave machine and to a method for manufacturing same. In particular, the invention relates to a polyphase travelling wave machine which comprises a stator and a rotor, with at least one stator coil and/or one rotor coil being arranged in at least one groove of the stator or the rotor, respectively, the coil projecting from the groove at both sides in a longitudinal direction under the formation of a coil head, and the cross section of the coil in the area of the respective groove differing from the cross section of the coil in the area of the coil head. Such a machine is known from DE 43 21 236 C1.
Such travelling wave machines (asynchronous, snychronous, rotary, or linear machines) are known in the state of the art, with the term xe2x80x9ctravelling wave machinesxe2x80x9d covering both motors and generators. Herein, the coils are formed by wound wire artefacts. Due to the fact that the wires must be insulated against each other and generally have a circular cross section, the space factor of the grooves (overall wire cross section/groove cross section) amounts to approx. 35% to 40%. Due to the fact that in wire coils which are wound in such a manner it is not predictable which windings of the wound wire coils come to lie adjacent to each other the insulation layer must at least have the dielectric strength of the maximum rated voltage which is applied to the winding.
The space factor can be improved within close limits by the use of braided or layed stranded wires in the manufacture of the coils, with the coils being pressed into the grooves.
Moreover, with wound coils the coil head which is required for assembling the coil into the groove projects relatively far beyond the groove on both sides. On the one hand, this contributes to an increased space requirement and, on the other hand, to increased ohmic losses in the coil.
FIG. 5 shows the stator of a synchronous machine according to the state of the art. As can be seen herein, a hollow cylindrical stator 10 is stacked from sheet metal. In the stator 10 grooves 16 which open radially to the inside are arranged coaxially with the longitudinal centre axis of the stator. In the grooves 16 coils 18a, 18b, 18c are arranged distributed over the circumference of the stator 10. In order to enable the insertion of the coils 18a, 18b, and 18c from a groove 16xe2x80x2 into a groove 16xe2x80x3 which is circumferentially spaced from same, each of the coils has a coil head 20 at the face end of the stator. Upon supplying an out-of-phase alternating current to the coils, a rotating magnetic field is built-up within which a rotor (not shown) is co-rotating. As is obvious the wire forming the coils have a constant (circular) cross section over the entire length, i.e. both in the area of the groove and in the area of the coil heads. This leads to the above explained drawbacks.
From DE 43 21 236 A1 a polyphase electrical machine with a winding from flat conductor form parts is known. A major aspect, however, with this known machine is that a reduction in the conductor cross section is avoided in that in the transition from the groove into the winding head an increase in the conductor cross section towards the groove width is effected. At the joints, too, all of which are located on the winding head faces, a reduction in conductor cross section is avoided with this known machine in that the conductor form parts in the end areas are extended towards the groove. (See col. 2, lines 21 to 30 of DE 43 21 236 A1).
From DE 38 03 752 A1 a stator for a three-phase generator is known the stator laminations of which comprise grooves in which stator windings are arranged. The stator winding sections within the grooves have a rectangular cross section, and the stator winding sections which form the coil heads outside the grooves have a circular cross section (see FIG. 5 and associated description). The stator winding sections with the circular cross section are formed by hollow cylindrical conductors while the stator winding sections with the rectangular cross section are formed by compression of the hollow cylindrical conductor (see col. 6, lines 19 to 21, of DE 38 03 752 A1).
From GB 1 329 205 it is known to make the windings as cast bodies in which the end sections (protruding from the grooves) have a larger cross section than the conductor sections within the grooves (see page 1, lines 69 to 73, of GB 1 329 205).
The invention is based on the object to provide a travelling wave machine in which the space factor is higher and/or the coil heads protrude less from the grooves.
In order to solve this object, the initially described travelling wave machine according to the invention is further developed in that the ratio of the thickness of the stator or rotor coil, respectively, in the area of the coil head to the thickness of the stator or rotor coil, respectively, in the area of the groove corresponds to the product of the number of phases of the travelling wave machine and the number of holes of each coil.
Under the term cross section of the stator and the rotor coil both the shape and the surface content of the cross section is to be understood.
This ensures that the coils in the head area are not wider in a radial direction than the depth of the grooves.
The configuration according to the invention makes it possible to design the shape of the coil section inside the groove in such a manner that the space factor increases, while concurrently there is the possibility to reduce the axial extension of the coil head through a suitable design of the winding in this area.
According to the invention, the cross section of the stator or rotor coil, respectively, in the area of the respective groove is larger than the cross section of the stator or rotor coil, respectively, in the area of the coil head. Thus, the ratio of the conductor proportion in the groove to the conductor proportion in the two coil heads increases considerably.
In a presently particularly preferred embodiment, the stator or rotor coil, respectively, is made from sheet metal material. With this, a particularly high space factor from approx. 60% to 80% can be achieved. In addition, the insulation of the individual windings can be designed relatively thin because there is a defined orientation of the individual windings relative to each other in the groove or in the area of the coil head, respectively, so that the maximum voltage drop between two neighbouring windings can be predetermined. Moreover, the heat resistance between the coil and the walls of the groove is considerably lower than in the state of the art. This allows the operation of the machine at a higher power. In addition, the assembly is simpler because the insertion of the individual sheet metal sections (or of coils formed from sheet metal sections) into the grooves requires less efforts than the introduction of preformed wire coils which have to be deformed upon the insertion into the groove. This facilitates the automation of the manufacturing process of the machine.
Because of the construction of the coils from sheet metal formed parts it is possible to design the grooves (with the same machine power) less deep than in the state of the art. This reduces the losses due to leakage inductances and the idle power requirement.
In a preferred embodiment the stator or the rotor coil, respectively, in the area of the groove is formed from multilayer stacked or folded sheet metal material, and in the area of the coil head from single-layer or fewer-layer sheet metal material.
According to the invention it is possible to manufacture the stator or the rotor coil, respectively, from copper or aluminium sheet metal material (or from alloys of the respective metal). This can considerably influence the weight or the volume of the machine. Moreover, the coil sections in the groove can consist of one material (e.g. copper or aluminium) and the coil sections forming the coil head can consist from another material (e.g. aluminium or copper).
Preferably, one winding each of the stator or the rotor coil, respectively, is formed by two essentially C-shaped sheet metal parts the open sides of which are facing each other and wherein one leg of the one C-shaped sheet metal part is connected with an opposite leg of the other C-shaped sheet metal part.